Aerosol exposure monitoring

ABSTRACT

A gas processing device such as an aerosol exposure monitor is configured for acquiring chronic data, acute data, or both simultaneously, and may include a pump and a noise dampening device. The noise dampening device may include an elastomeric membrane between an inlet chamber and an outlet chamber. In another aspect, an aerosol exposure monitor may include an impactor, a collection filter, and a nephelometer that includes a sample chamber integrated with an aerosol flow path associated with the impactor and collection filter.

RELATED APPLICATIONS

This application is the national stage of International Application No.PCT/US2012/062167, filed Oct. 26, 2012, titled “AEROSOL EXPOSUREMONITORING,” which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/551,660, filed Oct. 26, 2011, title “AERO6SOLEXPOSURE MONITORING,” the contents of both of which is incorporated byreference herein in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract no. U01ES016093 awarded by National Institute of Health. The government hascertain rights in the invention.

TECHNICAL FIELD

The present invention relates to personal level aerosol exposuremonitors and their uses, including aerosol exposure monitors that areportable, and personal level aerosol exposure monitors that are wearableby a user resulting from an inherently low burden design, forsimultaneous personal exposure monitoring applying both real time andintegrated filter analyses.

BACKGROUND

An aerosol exposure sensor and sampler is utilized to sample the aerosolin the immediate vicinity of the aerosol exposure monitor to enable thebreathing zone aerosol particles to be analyzed by any number ofdifferent techniques. The aerosol exposure monitor may be designed forindoor, outdoor, or personal use. A personal exposure monitor istypically designed to be worn by a person to sample the aerosol in thatperson's breathing zone.

Aerosol sampling may be done over a specified period of time(integration period). The aerosol exposure monitor may be configured toaerodynamically size and then collect particles during the integrationperiod, after which the collected particles are analyzed. As an example,the aerosol exposure monitor may include a sample inlet that leads to ahousing that contains a substrate. The substrate, for example a filter,is configured to enable particles of a desired size range to accumulatethereon. At the conclusion of the integration period, the substrate maybe removed and subjected to one or more types of destructive ornon-destructive analyses. This type of aerosol exposure monitor isuseful for enabling the acquisition of chronic or long-term exposuredata, but is limited by the fact that it is not able to perform any typeof measuring, sensing or detecting function in real time during theintegration period. That is, this type of aerosol exposure monitormerely collects a total population of one or more types of particlesover the integration period, after which one or more separate analysesmust be done to acquire data that may be integrated or averaged over theintegration period. This type of aerosol exposure monitor may be passiveor active. A passive monitor relies on natural aerosol flow applyingconvection rather than diffusion to size and collect the aerosol. Apassive monitor can be a low-burden (as to size, weight, and quietness)device, with little or no energy requirements, but does not collect themaerodynamically and collects so few particles that analytical techniquessuch as gravimetric mass analysis are either extremely limited orimpossible.

On the other hand, an active monitor includes some type of fluid-movingdevice (typically a pump) to positively establish a flow of aerosol intothe sizer of the active monitor. An active monitor may enable robustparticle collections, and also facilitates the inclusion of an aerosolimpactor in the active monitor and thus enables aerodynamic sizing ofthe particles being sampled. An active monitor, however, requires morepower than a passive monitor due to the need for operating the pump. Inthe case of a personal exposure monitor, batteries are utilized tosupply power and thus the additional power required for the pump limitsthe duration of the aerosol sampling period. Moreover, an active monitoris typically burdensome due to the inclusion of the pump, associatedplumbing, possibly an aerosol impactor, and in personal applications abattery pack. In addition to being larger and heavier than a passivemonitor, the active monitor has conventionally been noisy due to theoperation of the pump. The higher burden typically imposed by an activemonitor poses a significant wearing compliance problem in the case ofpersonal exposure monitors. In particular, the person to be monitoredmay be required to wear the active monitor during prescribed intervalsof time and during certain activities (which may include exercise orother activities involving a high level of motion and personal exertion)over the course of the sampling period. The acquisition of valid datafrom the personal exposure monitor thus requires “wearing compliance” bythe person. The higher the burden imposed by the active monitor, theless likely wearing compliance will occur. As an example, recent testingof personal monitors has shown that the majority of elementary agechildren are not comfortable with sensor systems that weigh more than300 grams and add more than 5 decibels to the environment.

Another type of aerosol exposure monitor may be configured to acquiredata from the aerosol being sample in real time during a prescribedsampling period. One example is a nephelometer, which typically measuresparticles in a fluid stream by illuminating the particles and detectingthe resulting light that is scattered from the particles. Unlike aturbidometer, which measures the effects of high concentrations ofparticles, a nephelometer is designed to measure both low and highconcentrations of particles. A nephelometer measures particleconcentration in real time and thus would be useful in the context of apersonal exposure monitor for acquiring peak exposure data. To beconvenient to carry and use, the nephelometer should be as small andcompact as possible. The nephelometer should also be highly sensitive tothe entire range of concentrations of particles the wearer mightencounter.

In view of the foregoing, there is an ongoing need for aerosol exposuremonitors that present extremely low burden and thus are useful aspersonal devices that are easily wearable by users. It would also beuseful to provide an aerosol exposure monitor capable of simultaneouslyacquiring both chronic and acute exposure data. There is also a need foractive aerosol exposure monitors capable of operating without excessivenoise.

SUMMARY

To address the foregoing problems, in whole or in part, and/or otherproblems that may have been observed by persons skilled in the art, thepresent disclosure provides methods, processes, systems, apparatus,instruments, and/or devices, as described by way of example inimplementations set forth below.

According to one implementation, an aerosol exposure monitor includes animpactor to size the aerosol; a sample chamber communicating with theimpactor and defining a fluid flow path along a first axis; a collectionfilter communicating with the sample chamber and removable from theaerosol exposure monitor; a pump communicating with the collectionfilter; a light source; a light detector; a first bore defining a firstoptical path from the light source to the sample chamber along a secondaxis; and a second bore defining a second optical path from the samplechamber to the light detector along a third axis, wherein the firstaxis, the second axis and the third axis are at angles to each other.

In some implementations, the collection filter may be contained in or bepart of a cassette that facilitates installation and removal of thecollection filter and avoids contamination of the filter material. Insome implementations, the first axis, the second axis and the third axisare mutually orthogonal to each other.

According to another implementation, a gas processing device includes ahousing; a sample inlet defining a gas flow path into the housing; apump disposed in the housing and including a pump inlet and a pumpoutlet; and a noise dampening device disposed in the housing. The noisedampening device includes an inlet chamber interposed between the sampleinlet and the pump inlet, an outlet chamber communicating with the pumpoutlet, and an elastomeric membrane interposed between and fluidlyisolating the inlet chamber and the outlet chamber.

In some implementations, the gas processing device is or includes anaerosol exposure monitor, which may include, for example, a particlecollection filter and/or a nephelometer.

According to another implementation, a method for monitoring aerosolincludes sizing particles of the aerosol by flowing the aerosol throughan impactor; collecting the sized particles by flowing the aerosolthrough a sample chamber along a first axis and through a collectionfilter, wherein the sized particles are collected on the collectionfilter, and wherein flowing the aerosol through the impactor, the samplechamber and the collection filter comprises operating a pumpcommunicating with an outlet side of the collection filter; irradiatingthe sized particles flowing through the sample chamber by directing anirradiating light into the sample chamber along a second axis angledrelative to the first axis, wherein scattered light propagates from theirradiated particles; and directing the scattered light to a lightdetector along a third axis angled relative to the first axis and thesecond axis to sense a total scattering potential of the sizedparticles.

According to another implementation, method for monitoring aerosolincludes operating a pump to establish a flow of aerosol into a housingand to a collection filter disposed in the housing, wherein aerosolparticles of a desired size range are collected on the collection filterand gas from the aerosol flows through the collection filter; flowingthe gas from an outlet side of the collection filter, through an inletchamber, and into an inlet of the pump; and flowing the gas from anoutlet of the pump, through an outlet chamber, and through an exhaustport open to a region outside the outlet chamber, wherein the outletchamber is adjacent to the inlet chamber and an elastomeric membrane isinterposed between and fluidly isolates the inlet chamber and the outletchamber, wherein the gas flowing through the inlet chamber contacts afirst side of the elastomeric membrane, and the gas flowing through theoutlet chamber simultaneously contacts a second side of the elastomericmembrane, and noise associated with the respective flows of the gasthrough the inlet chamber and the outlet chamber is reduced.

Other devices, apparatus, systems, methods, features and advantages ofthe invention will be or will become apparent to one with skill in theart upon examination of the following figures and detailed description.It is intended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a schematic view of an example of an aerosol exposure monitoraccording to an implementation of the present disclosure.

FIG. 2 is a schematic view of an example of a nephelometer according toan implementation of the present disclosure.

FIG. 3 is a schematic view of an example of an aerosol exposure monitoraccording to another implementation of the present disclosure.

FIG. 4 is a schematic (or functional block) diagram illustrating varioussignal processing functions that may be implemented by the aerosolexposure monitor illustrated in any of FIGS. 1-3.

FIG. 5 is a perspective view of an example of an aerosol exposuremonitor according to another implementation of the present disclosure,with a portion of its housing removed.

FIG. 6 is a top view of an assembly that includes an aerosol collectiondevice and a nephelometer, which may be included with the aerosolexposure monitor illustrated in FIG. 5.

FIG. 7 is a perspective view of the assembly with a portion cut-awayalong line A-A of FIG. 6.

FIG. 8 is an elevation view of the assembly with the same portioncut-away as in FIG. 7.

FIG. 9 is an exploded view of a noise dampening device, which may beincluded with the aerosol exposure monitor illustrated in FIG. 5.

FIG. 10 is a perspective view of the noise dampening device illustratedin FIG. 9.

FIG. 11 is a plot of measured sound level (dBA) of the aerosol exposuremonitor illustrated in FIGS. 5-10 as a function of the length (cm) of anexhaust tube of the noise dampening device illustrated in FIG. 9, for aflow rate of 0.5 liters/minute.

FIG. 12 is a functional diagram illustrating examples of processes forcalculating ventilation rate and potential dose.

FIG. 13 are plots of raw tri-axial (x, y and z values) accelerometerdata (in g units) over time (in sec) acquired from anaccelerometer-equipped aerosol exposure monitor worn by a person while(A) sitting at a computer, (B) walking at 2 mph on a treadmill, and (C)indoor cycling at 70 RPM.

FIG. 14 is an example of a screenshot generated by software configuredto provide an interface with the aerosol exposure monitor.

DETAILED DESCRIPTION

As used herein, the term “aerosol” generally refers to an assembly ofliquid or solid particles suspended in a gaseous medium long enough tobe observed and measured. The size of aerosol particles typically rangesfrom about 0.001 μm to about 100 μm. See Kulkarni et al., AerosolMeasurement, 3^(rd) ed., John Wiley & Sons, Inc. (2011), p. 821. Theterm “gaseous fluid” generally refers to a gas (or gaseous fluid, orgas-phase fluid). A gas may or may not contain liquid droplets or vapor,and may or may not contain aerosol particles (or particulates, orparticulate matter). An example of a gas is, but is not limited to,ambient air. An aerosol may thus be considered as comprising particlesand a gas that entrains or carries the particles. A “gas” may also referto an aerosol that has been filtered to remove particles from theaerosol. That is, an aerosol may be flowed through a filter designed toremove particles of a certain size range from the gas phase of theaerosol. As a result, the gas flowing from the outlet side of the filtermay be substantially free of particles, or at least substantially freeof particles of the size range intended to be blocked by the filter. Forpurposes of the present disclosure, the component of the pre-filteredaerosol that is allowed to pass through a filter will be referred to asa gas. Additionally, the term “fluid” is used herein interchangeablywith the term “gas” unless the context dictates otherwise.

FIG. 1 is a schematic view of an example of an aerosol exposure monitor(or monitoring apparatus, or monitoring device) 100 according to animplementation of the present disclosure. The aerosol exposure monitor100 generally includes an aerosol sample inlet 104, an aerosol sampleimpactor (or impactor assembly) 108, an aerosol sample collection filter(or filter assembly) 112, and a pump 116. All of the foregoingcomponents may be contained in a suitable housing or enclosure (notshown). The sample inlet 104 is open to the ambient environment outsidethe aerosol exposure monitor 100. The sample inlet 104 may be configuredsuch that the flow path of aerosol 120 entering the sample inlet 104 isturned at an angle (e.g., ninety degrees) before flowing into theimpactor 108. The right angle design smoothly transitions aerosol via alaminar flow regime from the front of the breathing zone of anindividual wearing the device into the impactor 108 with minimalinternal losses. FIG. 1 schematically depicts the order of succession ofthe components, with each component being in fluid communication withthe preceding component. The aerosol exposure monitor 100 isstructurally configured to establish (or define) a fluid flow path (or“gas” flow path) generally running from the sample inlet 104, throughthe impactor 108, through the collection filter 112, and into the pump116.

The impactor 108, often termed an aerosol impactor, particle impactor orintertial impactor, may have any configuration suitable foraerodynamically sizing particles in the sample aerosol flow wherebyparticles of a desired aerosol size range are collected on thecollection filter 112. The impactor 108 may be a multi-stage impactorconfigured for effecting sizing in successive stages, which may providegreater tolerance for high particle concentration by minimizing particlebounce. In the illustrated implementation, the impactor 108 is adual-stage impactor and hence includes a first impactor stage 124followed by a second impactor stage 128. The impactor 108 may beconfigured to minimize the impact of undesirable particle bounce betweenstages 124, 128 onto the subsequent collection filter 112. The sampleinlet 104 and impactor 108 may be configured as an assembly or modulethat is removable from the aerosol exposure monitor 100 to enableselection of different cut-points, for example PM_(2.5) (particulatematter of 2.5-micron size and smaller), PM₁₀ (particulate matter of10-micron size and smaller), etc. The sample inlet 104 (or an initialstage of the impactor 108) may include a coarse screening inlet (notshown) to prevent entry of large particles, insects, and other unwantedmatter. In one example of a dual-stage impactor assembly configured forPM_(2.5), the impactor 108 includes a 10-μm coarse inlet, followed by a4.0-μm cut-point first impactor stage 124, followed by a 2.5-μm secondimpactor stage 128. In one example of a dual-stage impactor assemblyconfigured for PM₁₀, the impactor 108 includes a 20-μm coarse inlet,followed by a 12-μm cut-point first impactor stage 124, followed by a10-μm second impactor stage 128. In some implementations, the impactorstages 124, 128 are configured for a cut-point accuracy of +/−0.5 μm.

The collection filter 112 may be any filter suitable for serving as asubstrate for collecting particles of the desired size range, and whichexhibits a low pressure drop for the flow rates contemplated for theaerosol exposure monitor 100. In some implementations, the ratedporosity of the collection filter 112 ranges from 2.0 to 3.0 microns(μm). In a specific example, the nominal porosity of the collectionfilter 112 is 3 μm. In some implementations, the composition of thecollection filter 112 is PTFE (polytetrafluoroethylene) although it willbe understood that other materials that are suitably free of backgroundcontamination may be suitable. The pressure drop through (across thethickness of) the collection filter 112 should be low enough to avoidexceeding the capacity of the pump 116 and to minimize consumption ofbattery power. In some implementations, the collection filter 112 isconfigured such that it exhibits a pressure drop of nominally less thanabout 5 cm of water (or less than about 2 inches H₂O) at a flow rate of0.5 liters/minute (and typical ambient temperature). In someimplementations, the collection filter 112 is configured such that itexhibits a pressure drop of nominally less than about 2.5 cm of water(or about 1 inches H₂O or less) at a flow rate of 0.5 liters/minute (andtypical ambient temperature). In one example, the collection filter 112is a commercially available, 3-μm porosity, 25-mm outside diameter PallGelman TEFLO® filter. In some implementations, the collection filter 112is removable from the aerosol exposure monitor 100. For this purpose,the collection filter 112 may be provided in the form of a filterassembly that includes a filter element (i.e., the actual filtermaterial) held in a filter cartridge. The collection filter 112 may beremoved by opening the housing of the aerosol exposure monitor 100 andhandling the filter cartridge, employing a tool such as a pair oftweezers if necessary or desired.

The pump 116 may be any small pump or micro-pump suitable for lowflow-rate operation, and which does not generate an excessive amount ofpulsing. The pump 116 may be configured to operate at a low flow ratethat allows the collection filter 112 to collect particles over asignificant duration of time, such as a day, a week, or longer. The lowflow rate also assists in avoiding turbulent flow along the flow path ofthe aerosol through the aerosol exposure monitor 100, minimizing thefluid velocity seen at the upstream surface of the collection filter 112and hence assisting in preventing significant internal losses andoverloading of the collection filter 112 when collecting particles overthe course of an extended sampling duration. The pump 116 may also beconfigured to operate continuously over the desired sampling period, orto operate cyclically to reduce consumption of battery power and thusenable an extended sampling period. In some implementations, the pump116 may be configured to operate at a flow rate ranging from 0.30 to0.60 lpm (liters per minute). In one specific implementation, the pump116 operates at a flow rate of 0.5 lpm. In one example, the pump 116 isa rotary vane pump. The pump 116 may generally include pump (or fluidmoving) components actuated by a motor. The motor may be in signalcommunication with circuitry (not shown) configured to control theoperation of the pump 116. The pump 116 may exhaust into an interior ofthe aerosol exposure monitor 100 or to an outlet provided by the housingof the aerosol exposure monitor 100.

The provision of the pump 116 renders the aerosol exposure monitor 100an active device, requiring electrical power beyond that needed tooperate the electronic circuitry and other active components providedwith the aerosol exposure monitor 100. The pump 116, however, activelyestablishes a controlled fluid flow through the aerosol exposure monitor100, thus facilitating the use of the impactor 108 upstream of thecollection filter 112. The low flow rate and optional cyclical operationof the pump 116 minimize the additional power consumed by the aerosolexposure monitor 100. The aerosol exposure monitor 100 may include an ACadapter to enable line power to be supplied from a wall outlet or otherexternal power source, and/or may include a universal serial bus (USB)or other suitable connection to enable power to be supplied from acomputing device, and/or may include an interface configured to receivebatteries of standard design. In some implementations, the pump 116 andassociated circuitry utilize only a small number of batteries, forexample three AA-size batteries and optionally a coin-type battery forbackup power. In some implementations, the aerosol exposure monitor 100may be configured for optional connection to an external battery pack toextend the duration of the sampling period.

In operation, the aerosol exposure monitor 100 may be activated manuallyby the user by pressing an ON button. Optionally, the aerosol exposuremonitor 100 may include timing circuitry configured for activating theaerosol exposure monitor 100 automatically according to a predeterminedschedule. Optionally, the aerosol exposure monitor 100 may include awireless transceiver to enable the aerosol exposure monitor 100 to beactivated remotely. In all cases, activation/deactivation of the aerosolexposure monitor 100 starts/stops the pump 116. The pump 116 establishesa flow of aerosol from the ambient into the aerosol exposure monitor 100via the sample inlet 104, and through the aerosol exposure monitor 100along the flow path described above. Particles of the aerosol are sizedby the impactor 108, and the remaining particles are accumulated on thecollection filter 112. The period of operation, i.e., the duration ofaerosol sampling and concomitant particle collection, may be anyspecified duration such as, for example, a day, a week, or longer. Oncesampling is completed, the aerosol exposure monitor 100 may bedeactivated manually or automatically. The collection filter 112 maythen be removed from the aerosol exposure monitor 100 and subjected toany desired destructive or non-destructive analysis of the collectedparticles known to persons skilled in the art or later developed, suchas gravimetric analysis, speciation analysis, chemical analysis,spectroscopic or spectrometric analysis, crystallographic analysis, etc.The analysis (or analyses) may entail any qualitative or quantitativedetermination of interest such as, for example, concentration ofparticles over time, personal level of exposure to particles,characterization of particles (e.g., size distribution, morphology,composition, toxicity, identification of particles), etc. The removedcollection filter 112 may be replaced with a new collection filter 112and the aerosol exposure monitor 100 may thereafter be re-deployed insubsequent sampling operations. The collection filters 112 utilized inthis implementation may be housed in a cassette to minimizecontamination from handling. Optionally, the individual impactorsurfaces of the respective impactor stages 124, 128 may be removed toenable analysis of the particle sizes captured by the impactor surfaces.

In the implementation described thus far, the aerosol exposure monitor100 may be characterized as being or including an aerosol collectiondevice (or aerosol sizing and collection device, or particle collectiondevice) 150. The aerosol collection device 150 may include the sampleinlet 104, impactor 108, collection filter 112, and pump 116 asdescribed above. In another implementation, the aerosol exposure monitor100 may also include a nephelometer 160 that is integrated with theaerosol collection device 150 to measure concentrations of the aerosolsized by the impactor 108. The nephelometer 160 is schematicallyillustrated in FIGS. 1 and 2. The nephelometer 160 includes a lightsource 164, a light trap 168, and a light detector 204. To facilitateintegration of the nephelometer 160 with the aerosol collection device150 and to provide a sample volume for the nephelometer 160, in theillustrated example the aerosol exposure monitor 100 includes a samplechamber 172 interposed between the impactor 108 and the collectionfilter 112. Accordingly, the aerosol exiting the impactor 108 (or thelast impactor stage) flows through the sample chamber 172 and to thecollection filter 112 along a first axis generally depicted by arrows174, 176 in FIG. 1. Insofar as the sample chamber 172 is part of thefluid flow path through the aerosol collection device 100 and also partof the optical path through the nephelometer 160, the sample chamber 172may be characterized as being a component of either or both of theaerosol collection device 150 and the nephelometer 160.

The light source 164 may be any device for generating a beam ofirradiating light 182 that propagates at a wavelength (or peakwavelength) for suitable for nephelometry. As examples, the light source164 may be a light emitting diode (LED) or a laser diode (LD). In someimplementations, the light source 164 emits irradiating light 182 at awavelength ranging from 300 to 800 nm. In one specific implementation,the light source 164 emits irradiating light 182 at a wavelength of 785nm. In operation, the beam of irradiating light 182 propagates into thesample chamber 172 along a second axis that is at an angle to the firstaxis along which the aerosol flows. In some implementations, the secondaxis is orthogonal to the first axis. The light trap 168 is locatedalong the second axis on the side of the sample chamber 172 opposite tothe light source 164 (i.e., on-axis with the light source 164).Accordingly, any portion 184 of the irradiating light propagatingthrough the sample chamber 172 without being scattered by the aerosolwill enter the light trap 168. The light trap 168 may, for example, be achamber defined by opaque or anti-reflective surfaces, and/or mayinclude geometries or structures configured for trapping light asappreciated by persons skilled in the art. Hence, the unscatteredportion 184 of the irradiating light passing through the sample chamber172 is absorbed by the light trap 168 and is not reflected back into thesample chamber 172, thereby minimizing the possibility that theunscattered light 184 interferes with the measurement of the scatteredlight and hence improving the sensitivity and detection limits of thenephelometer 160. Apertures (not shown) along the optical path may alsobe sized and positioned to minimize interference with the desiredmeasurement. To minimize noise in the detection signal, the light source164 may be pulsed so that the zero-signal level of the light detector204 may be measured and accounted for frequently. Optionally, thenephelometer 160 may include an additional light detector (not shown)positioned to monitor the intensity of the irradiating light 182 fromthe light source 164 or the unscattered light 184 from the samplechamber 172, and thus assess the performance of the light source 164.

FIG. 2 is a schematic view of the nephelometer 160 from the perspectiveof the top of the sample chamber 172, i.e., with the first axis alongwhich fluid flows directed into the drawing sheet. Light 208 scatteredby the aerosol in the sample chamber 172 is transmitted to the lightdetector 204 at an angle (e.g., ninety degrees) relative to the beam ofirradiating light 182, i.e., along a third axis that is at an angle tothe second axis as well as the first axis. Due to the compactness of thenephelometer 160, reflective surfaces or components on the side of thesample chamber 172 opposite to the light detector 204 are not needed intypical implementations, but may be included if desired. In someimplementations, to increase sensitivity the irradiating light 182 iscollimated, but not necessarily focused, and extends across the entiresample chamber flow path. As a result, the irradiating light 182 createsan expanded, generally cylindrical particle sensing volume 212 withinthe sample chamber 172, as opposed to a line or point generated by aconventionally focused laser beam. In a typical implementation, thecross-section of the generally cylindrical particle sensing volume 212is oval- or elliptical-shaped, i.e., particle sensing volume 212 isshaped as an elliptic cylinder. This configuration in turn produces awide, two-dimensional (rectilinear- or rectangular shaped) source ofscattered light 208 in the sample chamber 172 for capturing by the lightdetector 204. The expanded beam may also lower the limit of detection(LOD) of the nephelometer 160, and render the nephelometer 160 lesssensitive to vibration. In some implementations, the generallycylindrical sensing volume 212 has a length ranging from 8.0 to 12.0 mmand a diameter (or major axis in the case of an ellipticalcross-section) ranging from 0.5 to 2.0 mm. As illustrated in FIG. 2, thescattered light 208 may be collected by optics 216 (e.g., one or morelenses of appropriate design) before being transmitted to the lightdetector 204.

The light detector 204 may be any detector suitable for collecting lightin nephelometry applications. As examples, the light detector 204 may bea photodiode, an avalanche photodiode, or other type of compact lightdetector. The light detector 204 may be configured to take advantage ofthe rectangular-shaped beam of scattered light 208 emitted from thesample chamber 172 by having as wide a sensing area as possible in theavailable space. Accordingly, in some implementations, the lightdetector 204 includes a rectilinear-shaped (e.g., rectangular-shaped)active sensing area. This configuration enables a more complete captureof the scattered light 208 while minimizing the space needed for theoptics. In one example, the size of the sensing area is 2 mm by 3 mm.One non-limiting example of a suitable light detector 204 is ablue/green enhanced photodiode-preamplifier available as model no.ODA-6WB-500M from Opto Diode Corp., Newbury Park, Calif.

In operation, the nephelometer 160 may be operated simultaneously withthe aerosol collection device 150, whereby nephelometric data (e.g.,total scattering potential) is collected in real time and in situ whileparticles are being sized and collected by the collection filter 112.The combination of the nephelometer 160 and the aerosol collectiondevice 150 enables both acute and chronic exposure data to be collectedsimultaneously. That is, the nephelometer 160 measures acute responses(e.g., minimum or peak levels of exposure) in real time while theaerosol collection device 150 enables the acquisition of chronic(long-term) data that may be integrated or averaged over the totalsampling period (e.g., day, week, etc.). By enabling the collection oftotal aerosol over time as an integral part of the optical bench of thenephelometer 160, the aerosol exposure monitor 100 is able to collectacute and chronic exposure data without losing any of the aerosol beingsampled, i.e., there are no internal sample losses. This approachprovides a gravimetrically-based calibration against which to normalizethe concurrent mathematical integration of the simultaneous real-timedata file. Data from the light detector 204 may be logged in a memory ofthe aerosol exposure device 100 and later downloaded to a computingdevice for analysis. In some implementations, the nephelometer 160 has adynamic range of 2 to 10,000 μg/m³ and a resolution of 1 μg/m³, i.e., isable to detect a 1 μg/m³ change in concentration.

It will also be noted that gravimetric data acquired from the collectionfilter 112 may be utilized as an accurate referee calibration for thenephelometer 160. That is, the integrated real-time data concentrationby definition should equal the gravimetric filter calibration.

FIG. 3 is a schematic view of an example of an aerosol exposure monitor(or monitoring apparatus, or monitoring device) 300 according to anotherimplementation of the present disclosure. The aerosol exposure monitor300 generally includes an aerosol collection device, a pump (such as,for example, the pump 116 described above and illustrated in FIG. 1),and a noise dampening device (or gas flow pulsation and noise dampeningdevice) 304. In some implementations, the aerosol collection deviceincludes a sample inlet and a collection filter (e.g., the sample inlet104 and collection filter 112 described above and illustrated in FIG.1). In some implementations, the aerosol collection device maycorrespond to the aerosol collection device 150 described above andillustrated in FIG. 1. The aerosol exposure monitor 300 may also includea nephelometer, which may correspond to the nephelometer 160 describedabove and illustrated in FIGS. 1 and 2 and which thus may be integratedwith the aerosol collection device in the manner described above andillustrated in FIGS. 1 and 2.

The noise dampening device 304 may include an inlet chamber 306, anoutlet chamber 308, and an elastomeric (or deformable) membrane 310interposed between and fluidly isolating the inlet chamber 306 and theoutlet chamber 308. The inlet chamber 306 is in fluid communication withthe aerosol collection device 150, such as the outlet side of thecollection filter 112 in. For this purpose the inlet chamber 306 mayinclude a first port 314, which may, for example, be configured as aconnector that is coupled to a suitable fluid conduit 316 (e.g., atube). The inlet chamber 306 is also in fluid communication with aninlet 318 of the pump 116, which may be accomplished via conduit 320connected to a second port 322 of the inlet chamber 306. The outletchamber 308 is in fluid communication with an outlet 326 of the pump116, which may be accomplished via a conduit 328 connected to a thirdport 330 of the outlet chamber 308. The outlet chamber 308 is also influid communication with a fourth port (exhaust port) 334. The fourthport 334 may be open to an interior of the aerosol exposure monitor 300,or may be connected to a conduit (exhaust tube 336) and filtered ifthere is concern that emissions from the pump may cross-contaminate thenephelometer or filter collection systems. This exhaust tube 336 may beopen to the interior of the aerosol exposure monitor 300 or maycommunicate with an opening leading to the outside of the aerosolexposure monitor 300. The noise dampening device 304 thus establishes(or defines) an inlet flow path through the inlet chamber 306 directedinto the pump 116, and an outlet (or exhaust) flow path through theoutlet chamber 308 directed out from the pump 116.

The elastomeric membrane 310 serves as the boundary between the inletchamber 306 and the outlet chamber 308, and hence is exposed to thefluid flowing through inlet chamber 306 and the fluid flowing throughthe outlet chamber 308. For this purpose, the elastomeric membrane 310may be configured as a planar structure or sheet. The elastomericmembrane 310 may have any suitable shape, such as a rectilinear or otherpolygonal shape, or a circular or other rounded shape. The shape of theelastomeric membrane 310 may be the same as or similar to that of theinlet chamber 306 and the outlet chamber 308. The size of theelastomeric membrane 310 may depend on the size of the inlet chamber 306and the outlet chamber 308, in that the elastomeric membrane 310 shouldbe large enough to serve as a complete boundary between the inletchamber 306 and the outlet chamber 308. In one example, the elastomericmembrane 310 is a square having one-inch sides and a thickness of 0.010inch. In other examples, the area of the elastomeric membrane 310 mayrange from 5.0 to 15.0 cm, and the thickness may range from 0.125 to 0.5mm.

The elastomeric membrane 310 is exposed to the pressure pulsations andacoustical vibrations generated by the flow of gas in both the inletchamber 306 and the outlet chamber 308. The elastomeric membrane 310 hasbeen found to be highly effective in dampening these pulsations andvibrations and minimizing the system burden caused by the pump noiselevel. Without wishing to be bound by any particular theory at thepresent time, it is believed that dampening effectiveness may beattributed to the flexibility of the elastomeric membrane 310, and itsinterposition between the respective gas flows in the inlet chamber 306and the outlet chamber 308 whereby pressure and acoustical wavespropagating to one side of the elastomeric membrane 310 may partially orwholly cancel out pressure and acoustical waves propagating to theopposing side of the elastomeric membrane 310. In one non-limitingexample, a composition of the elastomeric membrane 310 found to exhibiteffective dampening is silicone rubber. It will be understood, however,that other compositions may also be suitable for functioning as theelastomeric membrane 310 in the presently disclosed noise dampeningdevice 304.

As also illustrated in FIG. 3, the noise dampening device 304 mayinclude a fluid filter 342 spanning the cross-sectional flow area of theinlet chamber 306 to prevent any particles in the gas stream fromentering the pump 116. Alternatively or additionally, the noisedampening device 304 may include another fluid filter 344 spanning thecross-sectional flow area of the outlet chamber 308 to prevent anyparticles in the gas stream discharged from the pump 116 fromcontaminating the interior of the aerosol exposure monitor 300. Thefluid filter 342, 344 should have a composition that does not undulyrestrict gas flow. In one example, the fluid filter 342, 344 is an opencell polymeric foam such as an open cell polyurethane foam (PUF). In oneexample, the cross-sectional area of the fluid filter 342, 344encountered by the flowing gas is 1.4 inches in length and 0.25 inch inheight. Without wishing to be bound by any particular theory at thepresent time, it is proposed that the provision of one or more fluidfilters 342, 344 as described and illustrated herein may serve a role inthe noise attenuation achieved by the noise dampening device 304.

As further illustrated in FIG. 3, the noise dampening device 304 may beutilized as a housing or enclosure for containing one or more sensorsconfigured to measure one or more properties of the gas flowing throughthe aerosol exposure monitor 300. Typically, such properties are moreaccurately measured upstream of the pump 116, and thus the sensors maybe located so as to be exposed to the gas flowing through the inletchamber 306. In the illustrated example, a temperature sensor 348 and arelative humidity (RH) sensor 350 are located in or at the inlet chamber306. The temperature sensor 348 and RH sensor 350 may be placed insignal communication with the electronics of the aerosol exposuremonitor 300 by any suitable means. For example, the temperature sensor348 and RH sensor 350 may be provided in the form of chips or otherstructures that are mounted to a printed circuit board (PCB) of theaerosol exposure monitor 300. In this case, the temperature sensor 348and RH sensor 350 may protrude through cut-outs formed in the side ofthe noise dampening device 304 facing the PCB. Appropriate seals may beprovided at the interfaces between the temperature sensor 348 and RHsensor 350 and their respective cut-outs to prevent fluid loss from thenoise dampening device 304. In alternative implementations, thetemperature sensor 348 and RH sensor 350 may be positioned in-line withthe fluid flow path at locations outside of the noise dampening device304.

Data from the temperature sensor 348 and RF sensor 350 may be logged ina memory of the aerosol exposure monitor 300 and utilized—either duringoperation or subsequently after downloading the data to a computingdevice—to correct the nephelometry data generated by the light detector204, i.e., to compensate for temperature and RH. This data may also beutilized in real time by the processing electronics of the aerosolexposure monitor 300 to control or adjust the pump 116 and therebycontrol or adjust the flow rate through the aerosol exposure monitor300. This data may also be utilized as quality control (QC) data toindicate the operating conditions that transpired during the samplingperiod.

As also illustrated in FIG. 3, the aerosol exposure monitor 300 mayinclude one or more pressure sensors. In the specific example, a firstdifferential pressure sensor 354 is utilized to monitor the flow rate ofgas through the aerosol exposure monitor 300 during operation of thepump 116. For this purpose, respective ports 356, 358 of the firstdifferential pressure sensor 354 may be placed in fluid communicationwith the inlet and outlet sides of an orifice 362 located downstream ofthe collection filter 112. The differential pressure data produced bygas flow through this orifice 362 may be utilized in real time as ameans for controlling the flow rate during operation of the pump 116,and this differential pressure data may also be logged in memory forlater downloading as QC data to a computing device to indicate theoperating conditions that transpired during the sampling period. Also, asecond differential pressure sensor 364 is utilized to monitor thecondition of the sample inlet 104 and the collection filter 112, i.e.,to determine whether the sample inlet 104 was blocked or obstructedduring operation and the rate of aerosol buildup on the collectionfilter 112 and thus identify short periods of significantly highloading. For this purpose, one port 366 of the second differentialpressure sensor 364 may be placed in fluid communication with the fluidflow path at a point downstream of the collection filter 112, whileanother port 368 is open to the interior of the aerosol exposure monitor300 to measure ambient pressure. The pressure data from the seconddifferential pressure sensor 364 may be utilized in real time toindicate an alarm condition and/or to automatically terminate thesampling process if the pressure drop is too large to maintain adequateflow rate control. The pressure data from the second differentialpressure sensor 364 may also be logged in memory for later downloadingas QC data to a computing device to indicate the operating conditionsthat transpired during the sampling period.

As also illustrated in FIG. 3, the aerosol exposure monitor 300 mayinclude one or more accelerometers for monitoring motion of the aerosolexposure monitor 300 along one or more directions (axes). In theillustrated example, a single tri-axial accelerometer 380 configured formeasuring acceleration in three directions is provided. Theaccelerometer 380 may be provided in the form of a microfabricated orMEMS-based chip that is mounted to the PCB of the aerosol exposuremonitor 300. One example of a suitable accelerometer 380 is an Okidata8953 accelerometer. The data produced by the accelerometer 380 may belogged in memory for later downloading as QC data to a computing device.In implementations where the aerosol exposure monitor 300 is utilized asa personal level exposure monitoring device, the accelerometer data maybe utilized to provide an indication of wearing (protocol) compliance,i.e., to verify that the user was wearing the aerosol exposure monitor300 during the time periods called for during the sampling period. Theaccelerometer data may also be utilized to determine the activities inwhich the user was engaged during the sampling period (e.g., personalenergy expenditure associated with sitting, walking, exercising, etc.),and this data may be correlated with the exposure data recorded by thelight detector 204 over the same sampling period. In implementationswhere the aerosol exposure monitor 300 is utilized as a stationarydevice in an indoor or outdoor setting, the accelerometer 380 may beutilized as a QC or security measure to determine whether the aerosolexposure monitor 300 was moved accidentally or without authorization.

In other implementations, FIG. 3 more generally represents a gasprocessing device (300) of any type whose operation entails active gasflow through the gas processing device and which may benefit from thepulse and/or noise dampening functionality of the noise dampening device304. The gas processing device generally includes a housing (not shown),a sample inlet providing flow communication into the housing, and a pumpand the noise dampening device 304 disposed in the housing. The gasprocessing device may include fluid circuitry (or plumbing) and one ormore types of instruments, detectors, sensors and the like communicatingwith the gas flow path through the housing. In addition to an aerosolexposure monitor, aerosol collection device, nephelometer such asdescribed by example above, other examples of the gas processing devicemay be (or be part of) any other type of instrument that acquires datafrom aerosols, or a gaseous sample introduction device that supplies thesample to a downstream instrument or reaction vessel, or a spectrometricinstrument (e.g., gas chromatograph), a spectroscopic instrument (e.g.,a Raman spectroscopic instrument), etc.

FIG. 4 is a schematic (or functional block) diagram 400 illustratingvarious signal processing functions that may be implemented by theaerosol exposure monitor 300 (or 100). Persons skilled in the art willappreciate that various functions (modules, circuitry, etc.) illustratedin FIG. 4 may be implemented by hardware (or firmware), software, orboth. Moreover, it will be appreciated that many of the functionsillustrated in FIG. 4 may be implemented by circuitry provided on a PCBcontained in the housing of the aerosol exposure monitor 300. In FIG. 4,an electronic controller 402 is representative of one or moremicrocontrollers, microprocessors, application specific integratedcircuits (ASICs), digital signal processors (DSPs), or the like; a realtime clock; sensor input/output (I/O) interfaces; analog-to-digitalconverters (ADCs), digital-to-analog converters (DACs); programmablememory; data logging memory; and selectable parameter settings. In someimplementations, the electronic controller 402 includes a 16 MB onboardmemory and an 8 MHz processor.

The electronic controller 402 may communicate with a power managementmodule 406, which may also communicate with a real time clock battery408 and a system battery pack 410. The electronic controller 402 mayalso communicate with one or more user interfaces such as, for example,LED indicators 414, a small display screen 416 such as a liquid crystaldisplay (LCD) screen, and pushbuttons 418. The electronic controller 402may also optionally communicate with a wireless transceiver 420. Theelectronic controller 402 may also communicate with a data communicationinterface 424 such as a universal serial bus (USB) interface, which maybe connected to a computing device 426 for downloading and uploading ofdata. For example, software executed by the computing device 426 may beutilized to process and display data received from the aerosol exposuremonitor 300 (or 100) subsequent to a sampling operation, and/or to setoperating parameters prior to a sampling operation. Optionally, thecomputing device 426 may also communicate with a power converter 430(e.g., USB interface) to provide power to the power management module406. As another option, an AC power adapter 432 may communicate with thepower converter 430 to provide line power from an external power source.The electronic controller 402 may also communicate with one or moreoutputs such as, for example, audio and/or visual alarms 436, a pumpdrive 438 for controlling the pump 116, and the light source 164 forcontrolling ON/OFF cycling. The electronic controller 402 may alsocommunicate with one or more inputs to receive data therefrom, and thepower management module 406 may communicate with one or more inputs toprovide power if necessary for their operation. Examples of such inputsmay include, but are not limited to, the first differential pressuresensor 354, the second differential pressure sensor 364, the temperaturesensor 348, the RH sensor 350, battery voltage check 442, the lightdetector 204, the accelerometer 380, and an optional GPS receiver 444.It can be seen that various types of QC data may be collected and storedby the electronic controller 402 and made available for download to thecomputing device 426, thereby enabling robust post-collectionvalidation.

The aerosol exposure monitor 300 (or 100) may be configured for use asan indoor monitor, an outdoor monitor, an in-vehicle monitor, or apersonal monitor. As an indoor or outdoor monitor, the aerosol exposuremonitor 300 may be placed in any fixed location where it is desired tosample aerosol in the immediate vicinity. As noted above, the aerosolexposure monitor 300 may be connected to a wall outlet or any othersource of external power. As an outdoor monitor, the aerosol exposuremonitor 300 may be placed in a suitable package, or its housing may bemodified, as necessary to withstand outdoor conditions. As a personalmonitor, the aerosol exposure monitor 300 may be configured so as to beeasily wearable by the user in an unobtrusive manner to ensurecompliance by the user in wearing the aerosol exposure monitor 300during the prescribed periods of operation. For instance, the aerosolexposure monitor 300 may be sized so as to be comfortably worn in apocket of the user, or in a small holder or bag comfortably worn by theuser. In one specific example, the maximum dimensions of the aerosolexposure monitor 300 are 2.7 inches in length, 1.6 inches in depth, and5.0 inches in height. When utilized as a personal monitor, the aerosolexposure monitor 300 will typically utilize a small number of batteriesas noted above. The burden to the user of wearing the aerosol exposuremonitor 300 may also be lessened by minimizing its weight. In someexamples, the aerosol exposure monitor 300 weighs less than 300 grams.In other examples, the aerosol exposure monitor 300 weighs less than 240grams. In other examples, the aerosol exposure monitor 300 weighs lessthan 220 grams. Reduced weight may be accomplished, for example, byemploying a light-weight yet robust material such as injection-moldedplastic for the housing and as many of the other structural componentsas possible. The various components housed in the aerosol exposuremonitor 300 may be arranged so as to balance its weight, therebyimproving the comfort of wearing the aerosol exposure monitor 300 andpromoting wearing compliance by the user.

FIGS. 5-10 illustrate an example of an aerosol exposure monitor 500according to another implementation. The aerosol exposure monitor 500may include many of the same or similar features as those describedabove and illustrated in FIGS. 1-4, and accordingly like referencenumerals designate like features in FIGS. 5-10. Specifically, FIG. 5 isa perspective view of the aerosol exposure monitor 500 with a portion ofits housing 504 removed. FIG. 6 is a top view of an aerosol samplingassembly 508 that includes the aerosol collection device and thenephelometer. FIG. 7 is a perspective view of the sampling assembly 508with a portion cut-away along line A-A of FIG. 6. FIG. 8 is an elevationview of the sampling assembly 508 with the same portion cut-away as inFIG. 7. FIG. 9 is an exploded view of the noise dampening device 304.FIG. 10 is a perspective view of the noise dampening device 304.

Referring to FIG. 5, the housing 504 may be configured to be opened inthe manner shown to enable removal of the collection filter 112,replacement of the batteries or other components, cleaning of theinterior, etc. The housing 504 may provide security features (not shown)to prevent its opening by the user or unauthorized personnel. Theremoved section (not shown) of the housing 504 may be configured formounting a set of batteries. A coin-type battery 512 shown in FIG. 5 maybe included to provide backup power. As previously noted, the aerosolexposure monitor 500 may be configured for continuous or ON/OFF cyclingoperation. In one example in which three AA batteries are employed, theaerosol exposure monitor 500 is capable of operating for 40 hours incontinuous mode and 168 hours in ON/OFF cycling mode. The exposuremonitor 500 may include various user interfaces as needed or desired,such as control buttons, a keypad, a display, LED indicators, ahigh-level alarm, etc.

The aerosol exposure monitor 500 may include a main PCB 516 thatprovides all or most of the electronics, and may also include one ormore additional PCBs 518, 520 as needed. In FIG. 5, the accelerometer380 has been arbitrarily located. FIG. 5 also shows the assembly of theaerosol collection device and the nephelometer, including the sampleinlet 104 which is located external to the housing 504. A port 524communicating with the flow orifice 362 (FIG. 7) below the removablecollection filter 112 is connected via a tube (not shown) to the firstport 314 of the inlet chamber 306 (FIG. 9) of the noise dampening device304. The second port 322 (FIG. 9) of the inlet chamber 306 is connectedvia a tube (not shown) to the inlet port 318 of the pump 116. The outletport 326 of the pump 116 is connected via a tube (not shown) to thethird port 330 of the outlet chamber 308 (FIG. 9) of the noise dampeningdevice 304. The fourth port 334 of the outlet chamber 308 is connectedto the exhaust tube 336 (FIG. 10) of the noise dampening device 304. Inthe present example, the exhaust tube 336 opens into the interior of thehousing 504. Another port 528 (FIG. 5) communicating with the outletside of the flow orifice 362 (FIG. 7) is connected via a tube (notshown) to a port 358 of the first differential pressure sensor 354. At apoint just below the removable collection filter 112, another port 532(FIG. 5) communicating with the inlet side of the flow orifice 362 isconnected via a tube (not shown) to another port 356 of the firstdifferential pressure sensor 354. This port 532 is also connected to aport 366 of the second differential pressure sensor 364. Another port(not shown) of the second differential pressure sensor 364 is open tocommunicate with the interior of the housing 504.

In some implementations, the tubing utilized to interconnect thedifferential pressure sensors 354, 364 to the various ports describedabove is capillary-sized tubing. In one non-limiting example, the insidediameter of the tubes is 0.010 inch or thereabouts. A very minutebidirectional fluid flow occurs in the tubes as pressure changes, and asthe pressures in the respective ports of the differential pressuresensors 354, 364 changes. Due to the restrictive, small inside diametersof the tubes, these pressure changes are pneumatically damped by thetubes and by the internal volume of the corresponding ports of thedifferential pressure sensors 354, 364. By this configuration, thesmall-diameter tubes act as resistors and the corresponding ports of theof the differential pressure sensors 354, 364 act as capacitors, greatlysmoothing the pressure spikes and thereby smoothing the electronicsignal produced by the differential pressure sensors 354, 364. It hasbeen found that this pneumatic damping of the pressure in the tubes ismore effective for obtaining a smooth average sensor reading thanelectronic damping of the signal by means of conventionalresistive/capacitive filter networks.

Referring to FIGS. 6-8, the sampling assembly 508 includes a cap 536that defines the sample inlet 104 and encloses the impactor 108. The cap536 defines one or more inlet openings (not shown) oriented to admitaerosol from a side direction. In this example, only one inlet openingis used. The inlet opening may include a screen (not shown). Aerosolflowing into the inlet opening is turned ninety degrees in an inletplenum 704 defined by the cap 536 and then flows through a coarse inletscreen 708, which scalps particles larger than a selected coarse size asdescribed earlier in this disclosure. In this example, the impactor 108includes a first impactor stage and a second impactor stage, whichrespectively include a first impactor plate 712 and a second impactorplate 716. The impactor plates 712, 716 may each have an oil retainedwithin a porous, sintered material or coating their surfaces to minimizeparticle bounce. In one non-limiting example, the oil is a silicone oil.

In operation, the pump 116 draws ambient aerosol into the opening of thesample inlet 104 and through the impactor 108. The aerosol passingthrough the coarse inlet screen 708 flows toward one or more passages720 radially offset from the central axis of the impactor 108. Particlestoo large to change momentum do not reach the radially offset passages720 and are consequently removed from the aerosol stream. The remainingaerosol flows through the radially offset passages 720 to the firstimpactor stage. The aerosol is then forced to change direction (e.g.,make a turn) and, in a laminar regime to minimize surface losses, flowsacross the first impactor plate 712 toward a central passage 724.Particles larger than the cut-point of the first impactor stage are notable to remain entrained in the aerosol stream and instead impact thefirst impactor plate 712. The remaining aerosol flows through thecentral passage 724 to the second impactor stage. The aerosol is thenforced to change direction yet again and flows across the secondimpactor plate 716 toward one or more radially offset passages 728.Particles larger than the cut-point of the second impactor stage are notable to remain entrained in the aerosol stream and instead impact thesecond impactor plate 716. The remaining aerosol then flows through theradially offset passages 728, through the sample chamber 172 and ontothe collection filter 112. In one example, the collection filter 112 hasan exposed area of filter material facing the sample chamber 172, andthe diameter of the exposed area ranges from 6 to 20 mm. The gas(filtered aerosol) is drawn through the flow orifice 362 below thecollection filter 112 and flows to the noise dampening device 304 anddifferential pressure sensors 354, 364 as described above.

The sampling assembly 508 also includes a nephelometer housing 604 thatencloses the light source 164, the light trap 168, the light detector204, optics 216, and various apertures. The sampling assembly 508includes PCBs 518, 520 on which the light source 164 and light detector204 are respectively mounted. The circuitry of the PCBs 518, 520communicates with the main PCB 516 via a ribbon cable 540 (FIG. 5). Aportion of the nephelometer housing 604 encloses a first bore 742 thatdefines the path of irradiating light from the light source 164. Anotherportion of the nephelometer housing 604 encloses an orthogonal secondbore 746 that defines the path of scattered light directed to the lightdetector 204.

The sample chamber 172 is shaped and sized such that the sample chamber172 is free or substantially free of turbulent flow—or, stated inanother way, the flow of the aerosol is entirely or substantiallylaminar from the outlet side of the impactor 108, through the samplechamber 172 and to the flow orifice 362. For the range of flow ratescontemplated (e.g., 0.5 liters/min) and depending on other operatingconditions, this may correspond to the Reynolds number characterizingthe aerosol flow being maintained below 1000, or below 250. In thepresent implementation, to maintain laminar flow the sample chamber 172is relatively large. In some implementations, the sample chamber 172 hasa total length from the impactor 108 to the collection filter 112ranging from 20 to 22 mm and a cross-sectional dimension ranging from 9to 14.4 mm. The cross-sectional dimension depends on the shape of thecross-section, for example an inside diameter in the case of a circularcross-section, a major axis in the case of an elliptical cross-section,etc. In one example, the sample chamber 172 has a total length of 20.98mm and internal diameters ranging from 13.50 mm to 10.00 mm. In theillustrated example, the sample chamber 172 has an upper tapered section752 and a lower section 754. The lower section 754 may have a constantinside diameter; for example, the lower section 754 may be cylindrical.In one example, the upper tapered section 752 has a length of 4.38 mm,an upper internal diameter of 13.50 mm, a lower internal diameter of10.00 mm, and a taper between the upper and lower internal diameters. Inthis example, the lower section 754 has a length of 16.60 mm and aninternal diameter of 10.00 mm. Moreover, the sample chamber 172 maygenerally be free of any edges or corners. Abrupt changes in geometryare avoided to prevent localized turbulence. The laminar flow minimizesthe pressure drop through the collection filter 112, minimizes thepossibility that the collection filter 112 will become overloaded,minimizes internal aerosol losses, and minimizes the power required fromthe batteries to run the pump 116 and thereby allows the pump 116 to runfor extended periods, e.g., a week or longer. Additionally, the laminarflow and the large sensing volume provided by the sample chamber 172improves the sensitivity and accuracy of the nephelometric datacollected.

As best shown in FIG. 7, the collection filter 112 includes a filterelement 762 held in a filter holder (or cartridge) 764. The filterholder 764 is designed to be removable from the assembly to facilitateanalysis of the particles captured by the filter element 762.

Referring to FIGS. 9 and 10, the noise dampening device 304 includes ahousing comprising two housing portions (or housing halves) 904, 906.The first housing portion 904 includes the first port 314 and the secondport 322, and the second housing portion 906 includes the third port 330and the fourth port 334. In assembled form, the elastomeric membrane 310is sandwiched between the two housing portions 904, 906 by any suitablemeans of securement. Four retainer clips 910 secure the assembly in thisexample. Seals such as gaskets may be provided to seal the interfacesbetween the elastomeric membrane 310 and the housing portions 904, 906.In assembled form, the first housing portion 904 and the elastomericmembrane 310 cooperatively form the inlet chamber 306, and the secondhousing portion 906 and the elastomeric membrane 310 cooperatively formthe outlet chamber 308. One or both housing portions 904, 906 mayinclude a fluid filter 914, only one of which is visible in FIG. 9. Inthe present implementation, each housing portion 904, 906 includes adiagonally oriented recess 922 and a set of posts 924 to locate and holdthe corresponding fluid filter 914. Also in the present implementation,the first port 314 and the second port 322 are oriented orthogonal toeach other, and the third port 330 and the fourth port 334 are likewiseoriented orthogonal to each other, with the first port 314 beingproximal to the fourth port 334 and the second port 322 being proximalto the third port 330. Accordingly, the fluid flow through the inletchamber 306 changes direction at the fluid filter 914, and the fluidflow through the outlet chamber 308 likewise changes direction at thefluid filter 914.

Also in the present implementation, the first housing portion 904 facesthe main PCB 516 (FIG. 5). The first housing portion 904 includes twocut-outs (or openings) 932, 934. The temperature sensor 348 and the RHsensor 350 are collocated on the main PCB 516 with the respectivecut-outs 932, 934, whereby the temperature sensor 348 and RH sensor 350may protrude into the inlet chamber 306 or at least be exposed to thefluid flowing therethrough, upstream of the pump 116. Seals (not shown)may be provided at the interface between the temperature sensor 348 andRH sensor 350 and the cut-outs 932, 934 to minimize fluid loss from theinlet chamber 306. It will be noted that the second housing portion 906may also nominally include the same cut-outs for purposes of loweringmanufacturing costs. These cut-outs (if present) may be blocked byplugs, covered by tape, or otherwise sealed to prevent fluid loss fromthe outlet chamber 308.

In some implementations, the exhaust tube 336 has a length ranging from1 to 15 cm, and an inside diameter ranging from 1 to 3 mm. Thedimensions of the exhaust tube 336 may influence the effectiveness ofthe noise dampening provided by the noise dampening device 304, asdiscussed below.

In one evaluation of the aerosol exposure monitor 500 illustrated inFIGS. 5-10, the total sound level at one meter away from the aerosolexposure monitor 500 during operation of the pump 116 at a flow rate of0.5 liters/minute was found to be 38 dBA (decibels, A-weighting), whichis not much higher (less than 3 dBA higher) than the typical backgroundsound level contemplated for a user. Therefore, the aerosol exposuremonitor 500 may be characterized as being very quiet in operation, whichis expected to promote wearing compliance by the user. FIG. 11 is a plotof measured sound level (dBA) of the aerosol exposure monitor 500 as afunction of the length (cm) of the exhaust tube 336 of the noisedampening device 304, for a flow rate of 0.5 liters/minute. Forcomparison, a data point is also shown for the sound level when theaerosol exposure monitor 500 is operated without the noise dampeningdevice 304. FIG. 11 demonstrates a significant reduction in sound levelwhen the noise dampening device 304 is employed, with a noise level ofonly 1 dBA or less above ambient being attainable. As noted earlier inthis disclosure, it has been found that children are not comfortablewith sensor systems that add more than 5 decibels to the environment. Bycomparison, it can be seen that the aerosol exposure monitor 500 whenprovided with the noise dampening device 304 may be operated at a noiselevel well below (by a factor of two or more) the noise level foundobjectionable by children. FIG. 11 also demonstrates that noisedampening may be optimized through selection of an appropriate lengthfor the exhaust tube 336.

In some implementations, the aerosol exposure monitor 500 (or 300) isconfigured to utilize the accelerometer data to calculate (or estimate,or predict) the ventilation rate (m³/min, or liters/min) of the wearerduring the sampling period. A strong correlation (e.g., R²=0.90) hasbeen found between accelerometer data and ventilation rate. In someimplementations, the aerosol exposure monitor 500 is configured toutilize the accelerometer data to calculate (or estimate, or predict)the potential dose (μg/min/kg, where kg is the unit of body weight ofthe wearer) to which the wearer was exposed during the sampling period.In some implementations, the aerosol exposure monitor 500 is configuredto utilize the nephelometer data (μg/m³) in conjunction with theaccelerometer data to make these calculations. FIG. 12 is a functionaldiagram illustrating examples of processes for calculating ventilationrate and potential dose. These calculations may be made, for example, inaccordance with an algorithm executed by hardware and/or software of theaerosol exposure monitor 500.

FIG. 13 are plots of raw tri-axial (x, y and z values) accelerometerdata (in g units) over time (in sec) acquired from anaccelerometer-equipped aerosol exposure monitor worn by a person while(A) sitting at a computer, (B) walking at 2 mph on a treadmill, and (C)indoor cycling at 70 RPM. The data were collected at a rate of 20 Hz,for five-second periods (a total of one hundred 0.05 s time steps). Asevident from the plots of the more energetic activities (B and C) theaccelerometer data exhibit distinctive patterns which, when combinedwith the signal resolution (about 0.02 g) of the accelerometer, may beutilized to identify the specific types of activity engaged in by theperson while wearing the aerosol exposure monitor and the aerosolexposure monitor is being operated to acquire particle exposure-relateddata. As noted above, the acquisition, storage and optional processingof both the accelerometer data and the exposure data may be performedon-board the aerosol exposure monitor. It can be seen that theaccelerometer data is acquired transparently to the person wearing theaerosol exposure monitor, and thus the person is not required tomaintain time-activity diaries.

FIG. 14 is an example of a screenshot generated by software configuredto provide an interface with the aerosol exposure monitor, typicallybetween sampling periods (e.g., when the aerosol exposure monitor is notbeing worn by a user during a sampling period in the case of a personalexposure monitor). For example, the software may reside in and beexecuted by a computing device. After the completion of a samplingperiod, the aerosol exposure monitor may be placed in communication withthe computing device, such as via a USB interface for example, and alldata acquired by aerosol exposure monitor may be uploaded to thecomputer device for use by the software. As shown in FIG. 14, thesoftware may be configured to merge the real-time concentration datawith real-time estimates of the ventilation rate to output potentialdose levels in μg/min/kg. As also shown, other types of data acquiredfrom the aerosol exposure monitor may be concurrently presented such as,for example, temperature, relative humidity, wearing compliance levelindication (e.g., worn, not worn), the body weight of the wearer, etc.As also shown, in addition to the “Nephelometer” other tabs providingdisplays of other types of the data may be included, such as an“Accelerometer” tab at which data similar to that shown in FIG. 13 maybe presented, and a “Pressure/Flow” tab at which data acquired byon-board pressure sensors (such as described above), mass or volumetricflow sensors, or the like may be presented.

In general, terms such as “communicate” and “in . . . communicationwith” (for example, a first component “communicates with” or “is incommunication with” a second component) are used herein to indicate astructural, functional, mechanical, electrical, signal, optical,magnetic, electromagnetic, ionic or fluidic relationship between two ormore components or elements. As such, the fact that one component issaid to communicate with a second component is not intended to excludethe possibility that additional components may be present between,and/or operatively associated or engaged with, the first and secondcomponents.

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation—the inventionbeing defined by the claims.

What is claimed is:
 1. An aerosol exposure monitor, comprising: animpactor; a sample chamber communicating with the impactor and defininga laminar fluid flow path along a first axis; a collection filtercommunicating with the sample chamber and removable from the aerosolexposure monitor; a pump communicating with the collection filter; alight source configured to generate a light beam that occupies a sensingvolume in the sample chamber, wherein the fluid flow path passes throughthe sensing volume along the first axis, and the light beam propagatesalong a second axis that is at an angle to the first axis; a lightdetector; a first bore defining a first optical path from the lightsource to the sensing volume along the second axis; and a second boredefining a second optical path from the sensing volume to the lightdetector along a third axis, wherein the first axis, the second axis andthe third axis are at angles to each other.
 2. The aerosol exposuremonitor of claim 1, comprising at least one of the following: a sampleinlet comprising an inlet opening configured such that the sample inletestablishes an inlet flow path that turns ninety degrees from the inletopening to the impactor; a light trap disposed on a side of the samplechamber opposite to the first bore; an accelerometer configured fordetecting motion of the aerosol exposure monitor along one or more axes;a differential pressure sensor configured for detecting a pressure dropacross an orifice between the collection filter and the pump; adifferential pressure sensor configured for detecting a pressure dropbetween an inlet side of the impactor and an outlet side of thecollection filter.
 3. The aerosol exposure monitor of claim 1, whereinthe impactor comprises a plurality of impactor stages, each successiveimpactor stage having a smaller cut-point than the other impactorstages.
 4. The aerosol exposure monitor of claim 1, wherein the samplechamber has a length between the impactor and the collection filterranging from 20 mm to 22 mm, and a cross-sectional dimension rangingfrom 9 mm to 14.5 mm.
 5. The aerosol exposure monitor of claim 1,wherein the pump is configured for providing a flow rate ranging from0.30 to 0.60 liters per minute.
 6. The aerosol exposure monitor of claim1, wherein the light source is configured according to at least one ofthe following: the sensing volume is cylindrical; the sensing volume iscylindrical, and has a length ranging from 8.0 to 12.0 mm and a diameterranging from 0.5 to 2.0 mm; the sensing volume is an elliptic cylinder.7. The aerosol exposure monitor of claim 1, wherein the light detectorcomprises a rectilinear sensing area communicating with the second bore.8. The aerosol exposure monitor of claim 1, comprising electroniccircuitry configured according to at least one of the following:electronic circuitry configured for collecting quality control dataduring operation of the aerosol exposure monitor; electronic circuitryconfigured for collecting quality control data during operation of theaerosol exposure monitor, wherein the quality control data are selectedfrom the group consisting of a flow rate of fluid through the collectionfilter, a pressure drop through the collection filter, a pressure dropfrom an inlet side of the impactor to an outlet side of the collectionfilter, a temperature of fluid flowing through the aerosol exposuremonitor, a relative humidity of fluid flowing through the aerosolexposure monitor, data produced by an accelerometer of the aerosolexposure monitor defining wearing compliance, a voltage level of abattery of the aerosol exposure monitor, GPS data pertaining to alocation of the aerosol exposure monitor, and a combination of two ormore of the foregoing; electronic circuitry configured for adjusting thepump based on a parameter selected from the group consisting of a flowrate of fluid through the collection filter, a pressure drop across anorifice following the collection filter, a pressure drop from an inletside of the impactor to an outlet side of the collection filter, atemperature of fluid flowing through the aerosol exposure monitor, arelative humidity of fluid flowing through the aerosol exposure monitor,and a combination of two or more of the foregoing.
 9. The aerosolexposure monitor of claim 1, comprising at least one of the following: anoise dampening device communicating with the pump; a noise dampeningdevice communicating with the pump, wherein the noise dampening devicecomprises an inlet chamber, an outlet chamber, and an elastomericmembrane interposed between and fluidly isolating the inlet chamber andthe outlet chamber, wherein the inlet chamber is interposed between thecollection filter and the pump inlet, and the outlet chambercommunicates with the pump outlet.
 10. A method for monitoring aerosol,the method comprising: sizing particles of the aerosol by flowing theaerosol through an impactor; collecting the sized particles by flowingthe aerosol through a sample chamber along a first axis and through acollection filter, wherein the sized particles are collected on thecollection filter, and wherein flowing the aerosol through the impactor,the sample chamber and the collection filter comprises operating a pumpcommunicating with an outlet side of the collection filter; irradiatingthe sized particles flowing through the sample chamber by directing anirradiating light into the sample chamber along a second axis angledrelative to the first axis, wherein the irradiating light establishes asensing volume in the sample chamber, the aerosol flows through thesensing volume along the first axis, and scattered light propagates fromthe irradiated particles; directing the scattered light from the sensingvolume to a light detector along a third axis angled relative to thefirst axis and the second axis to sense a total scattering potential ofthe sized particles; and a light source configured to generate a lightbeam that occupies a sensing volume in the sample chamber, wherein thefluid flow path passes through the sensing volume along the first axis,and the light beam propagates along a second axis that is at an angle tothe first axis.
 11. The method of claim 10, comprising at least one ofthe following: wherein the flow of aerosol out from the impactor,through the sample chamber, and to the collection filter issubstantially laminar; wherein the aerosol is flowed through thecollection filter at a total system pressure drop through the collectionfilter of 2 inches H₂O or less; wherein the aerosol is flowed throughthe collection filter at a flow rate ranging from 0.30 to 0.60liters/min.
 12. The method of claim 10, wherein directing theirradiating light into the sample chamber comprises at least one of thefollowing: establishing a cylindrical sensing volume of light in thesample chamber; establishing a cylindrical sensing volume of light inthe sample chamber, and the cylindrical sensing volume has a lengthranging from 8.0 to 12.0 mm and a cross-sectional dimension ranging from0.5 to 2.0 mm; establishing a cylindrical sensing volume of light in thesample chamber, wherein the cylindrical sensing volume has an ellipticalcross-section and the cross-sectional dimension is a major axis.
 13. Themethod of claim 10, wherein directing the scattered light to the lightdetector comprises directing the scattered light from the sample chamberas a beam having a rectilinear cross-section.
 14. The method of claim10, comprising acquiring particle concentration data from the lightdetector, and subjecting the collection filter to a particle analysis.15. The method of claim 10, comprising at least one of the following:operating an aerosol exposure monitor to size the particles, collect thesized particles, irradiate the sized particles and direct the scatteredlight, while a user is wearing the aerosol exposure monitor; operatingan aerosol exposure monitor to size the particles, collect the sizedparticles, irradiate the sized particles and direct the scattered light,while a user is wearing the aerosol exposure monitor, and acquiringaccelerometer data corresponding to movement of the user while wearingthe aerosol exposure monitor to provide an indication of activity of theuser during wearing of the aerosol exposure monitor near a breathingzone of the user; operating an aerosol exposure monitor to size theparticles, collect the sized particles, irradiate the sized particlesand direct the scattered light, while a user is wearing the aerosolexposure monitor, and acquiring accelerometer data corresponding tomovement of the user while wearing the aerosol exposure monitor toprovide an indication of activity of the user during wearing of theaerosol exposure monitor near a breathing zone of the user, andcalculating a ventilation rate (m³/min) of the user during wearing ofthe aerosol exposure monitor based on the accelerometer data,calculating a potential dose (μg/min/kg) of the user during wearing ofthe aerosol exposure monitor based on the accelerometer data and onparticle concentration data acquired from the light detector, orcalculating both the ventilation rate and the potential dose.